1. Field of the Invention
The invention relates to a semiconductor wafer processing system having remote plasma source. More particularly, the invention relates to a method for initiating and controlling an amount of power applied to a plasma within a remote plasma source (RPS).
2. Description of the Background Art
Dry etch processes are well known in the art of semiconductor manufacturing, and are used to remove material from a semiconductor wafer using a gas or vapor as the etchant. In a dry etch system, a process gas is exposed to an electromagnetic field to convert the process gas into a plasmatic state. The use of plasma is advantageous to etch processes because the energetic plasma facilitates rapid etching. In an etch system having a remote plasma source, the plasma is generated in a chamber that is separate from the process chamber wherein the semiconductor wafer is located. The plasma chamber (also known as an applicator) is driven with microwave energy (e.g., 2.5 GHz at 1500 watts) generated by a microwave source such as a magnetron. The plasma chamber and the process chamber are coupled to one another by a conduit. In this manner, the wafer is not exposed to the electromagnetic fields that produce the plasma. The amount of plasma used at any given time is controlled by controlling 1) the amount of process gas released into the electromagnetic field within the plasma chamber, and 2) the amount of electromagnetic energy this process gas is exposed to within the plasma chamber.
In presently available systems, a user selects a power level to be used to ignite and maintain the plasma. Unfortunately, the user could request a magnetron power that is too low to ignite a plasma. The prior art systems generally refuse to activate the magnetron power level that is deemed too low.
Therefore, there is a need in the art for a method and apparatus that allows the plasma to be used at power levels that heretofore were considered "too low" by igniting a plasma at a safe power level and then adjusting the power to a user defined level.